I want to install a 12V digital volt meter

Here's a multifunction (time/temperature/voltage) one that I just ordered a day or so ago. It appears to be going through the usual shipping process. (It hasn't actually shipped yet, just sitting in the "preparing for shipping" queue still...as is typical.)

Linky

I haven't decided yet if I'll have the thermometer measure the outside temperature or the fridge temperature. I'm leaning towards the outside temperature at the moment.